Process for melt-spinning of synthetic linear high polymers



16, 1967 G. E. BUSCHMANN ETALI 3,320,343

PROCESS FOR MELT-SPINNING OF SYNTHETIC LINEAR HIGH POLYMERS Filed Sept. 9, 1963 FIG. i PEG. 3

will! INVENTORS GERHARD BUSCHMANN HANS DIETER GOTTHARDT HANS KOCH United States Patent Ofiice 3,320,343 Patented May 16, 1967 3,320,343 PROCESS FOR MELT-SPINNING F SYNTHETIC LINEAR HIGH POLYMERS Gerhard Emil Buschmann and Hans-Dieter Gotthardt,

Rudolstadt, and Hans Koch, Leipzig, Germany, assignors to Veb Chemiefaserwerk Schwarza Wilhelm Pieck, Rudolstadt, Germany Filed Sept. 9, 1963, Ser. No. 308,619 3 Claims. (Cl. 264-176) The invention relates to a process for making threads and other products from synthetic linear polymers by melt-spinning.

It is known that the evenness of structures made by spinning through nozzles from inorganic or organic melts, e.g. from glass or polyamides, polyesters and the like, depends on the fixation of the solidifying point of the extruded threads in the cooling zone, which is mostly a gaseous zone. Fluctuations of flow in the cooling medium are likely to affect the extruded structures, particularly threads, which are drawn during the spinning process.

The elimination of undesirable disturbances in the flow of the cooling medium has been attempted by a number of devices which impart to the cooling medium a flow direction transversely, that is to say at right angles, to the thread axis when the thread is not deflected.

Another factor is that the flow of the cooling medium should be free of turbulence, i.e. should be laminar; this can be achieved with proper guide systems, similar to wind tunnels.

However, the use of all known devices was not capable of insuring the desired quality of the synthetic structures and of eliminating all factors which deteriorate the properties upon solidification; such factors are, e.g., thermal updraft, the influence of the upper and lower border zones of the blower, and the amount of the cooling medium passing through the cooling zone.

It is an object of the present invention to improve the method of melt-spinning of synthetic linear high polymers and of eliminating the harmful effect of uneven solidification in the cooling zone. Other objects and advantages of the present invention will become apparent from the following detailed description, in combination with the accompanying drawing.

The invention is based on the discovery that not only the optimum titer constancy, but also mechanical and elastic properties of the structures, particularly threads, are affected during the cooling and that all involved factors can be best influenced by a certain co-action of thermal and flow conditions.

The invention also takes care of providing particular means to eliminate flow disturbances at the upper edge, the lower edge, and the front edge of the cooling zone. Provision has further been made to counteract flow disturbances which are caused by the inherent movement of the threads in the direction of the thread axis, and by the updraft conditions occurring during the cooling, with detachment at the lateral borders of the stream of the cooling medium.

The present invention therefore relates to a process for the melt-spinning of synthetic linear high polymers such as polyamides, polyesters, polyurethanes, and so on, with a defined solidification of the shaped structures, preferably threads, in a stream of a gaseous or vaporous cooling medium.

According to the process of the present invention the stream of the cooling medium meets the non-deflected thread in a direction which is inclined to the direction of the thread, preferably at an angle of to 30 degrees with respect to the horizontal, the temperature of the cooling stream being between 15 and C. and the relative moisture 50 to 90%. The meeting between the cooling stream and the thread must be free of impact and of turbulence, and it takes place in a zone of overpressure. If the amount of cooling medium is maintained constant, the rate of flow in the cooling zone may be varied. A distribution system later to be described will provide for an even gas distribution throughout the chambers and the total current resistance will likewise remain unchanged.

The apparatus for carrying out the process of the in vention will now be more fully described with reference to the accompanying drawing, in which one embodiment of the device is shown by way of example.

In the drawing:

FIG. 1 is a side elevation, partly in section, along the line II of FIG. 3;

FIG. 2 is a view in section along line 22 of FIG. I; and

FIG. 3 is a front elevation, with parts broken away.

Referring now to the drawing, a gas distribution system 1 comprises a tubular admission member 2 and diffusor means with screen inserts 3. A pressure chamber is designated by 4 and is shut off by dilfusor means or resistances 5 consisting of screens on perforated sheets and of a honeycombed flow rectifier system 6 designated to provide impact-free and non-turbulent flow conditions in the cooling zone. Numeral 11 designates an inlet passage through which the cooling medium is introduced from a suitable source and through conventional ducts (not shown). At 12, a lateral flange is shown through which part of the cooling gas may be allowed to pass into the spinning room housing the apparatus, for conditioning the room temperature and/or moisture content. At 11, a constant gas input is maintained; the quantity of gas bypassing the chamber 4 at 12 regulates the flow rate within the pressure'chamber 4.

By the gas or air inlet distribution system 1, which may comprise a three-way cock or a throttle valve as schemetically shown at 13, the flow rate of the cooling medium in the spinning shaft may be varied without a change in the amount of gas withdrawn for an individual nozzle and without flutuation of the pressure in the chamber 4. This is also important for the dissipation of heat from the aggregates operating in the room during the spinning operation and for pressure equalization, if necessary.

The admission tube 2 with dilfusor system 3 secures an even velocity profile at the entrance of the cooling medium into chamber 4. For equalization of the gas current, the tube 2 is provided with the screen inserts 3 the size of which may be calculated by known fluid flow formula from the geometrical data.

The system of the plenum chamber 4 with the bordering diffusor screens on resistances 5 and the rectifier system 6 serve not only for pressure equalization (caused for instance by the compressor which builds up a certain preliminary pressure) but also for producing a predetermined velocity fiow profile. In order to keep the flow uniform in horizontal direction, the chamber has an almost rectangular cross-section. Toward the top end, the chamber has a decreasing cross section (as may be seen from FIG. 1) due to decreased flow requirement in the upper part of chamber 4, which is almost zero; the shape of the chamber is streamlined in accordance with the principle of Bernoulli.

The resistance of the member 5 depends on the desired maximum flow rate. The desired flow profile is effected by several screen layers or perforated sheets of desired length and mesh-size. One advantageous embodiment for a uniform velocity profile through screens 5 is the even taper of the chamber toward the top with approximately parallel side walls and with two to three layers of screens, placed at the distance of a few milli meters.

An almost impact-free admission of the flow is secured by the diffusion screens or resistances 5 into the rectifier system 6 which preferably consists of a system of honey combs adjusted at the desired inclination with respect to the direction of flow. At a flow rate of the cooling medium of about 20 to 40 crn./ s. a gradual increase in the inclination of the direction of the flow of the cooling medium with respect to the thread from a direction extending normally across the thread in the direction of thread movement to a direction which extends at about 15 to 25 degrees with respect to a straight line normal to the non-de-- fiected thread has proved advantageous for decreasing the updraft effect. In other words, the moving thread is initially engaged by cooling medium which fiows directly across the thread perpendicularly thereto, and as the thread continues to advance through the cooling zone the direction of inclination of the cooling medium with respect tothe thread constantly changes in the direction of thread movement until at the outlet end of the cooling zone the cooling medium flows across the thread at an angle of from l-30, preferably l25, with respect to a straight line which extends perpendicularly or normally across the non-deflected thread, and of course from the inlet end to the outlet end of the cooling zone the inclination of the cooling medium gradually increases between the limits where the cooling medium initially flows perpendicularly across the thread and finally flows across the thread at an angle of from -30" with respect to a straight line normal to the thread. Thus, where the thread moves downwardly, as shown in FIG. 1, the cooling medium will at the upper inlet end of the cooling zone, where the thread is initially received therein, flow horizontally across the vertical thread, and the direction of flow of the cooling medium is gradually inclined in a downward direction as the thread advances downwardly through the cooling zone until at the bottom outlet end of the cooling zone, where the thread leaves the latter, the cooling medium is inclined downwardly across the thread at an angle of between 10 and 30 with respect to a line extending horizontally across the thread.

FIG. 1 of the drawing shows the transition of the honeycombs from practically zero degrees slant at the connection 9 (top of the device), where the cooling medium flows horizontally across the thread, perpendicularly thereto, toward a predetermined maximum inclination (at the bottom of chamber 4) of, e.g., -25 degrees in a downward direction with respect to a straight line extending horizontally across the vertical thread.

As mentioned above, the combination of the resistance 5 and the rectifier system 6 secures an impact-free and non-turbulent flow in the desired direction. The length of the honeycomb structure system 6 which extends over the entire blowing surface is so chosen that the ratio formed by the square of the maximum diameter of a honeycomb transversely to the flow direction and to its length is less than twenty-fold of the ratio of the kinematic viscosity of the medium and its maximum velocity. This can best be expressed by the formula:

dg vis.

l V max.

wherein: D=depth of the system at XX; d=diameter; l=length;

The thickness of the walls of the honeycomb should be as small as possible. For this relation we provide: ratio of wall thickness to the quotient of the square of the free diameter of the honeycomb and the length of the same. smaller than 2 or 3 at the utmost.

Lateral confining walls 7 of the cooling zone serve for maintaining a turbulent-free flow. They are shaped concavely over the entire thread range and beyond in the direction from the shaft interior in order to prevent discontinuity of the current along the wall. The turning point lies behind the thread in the direction of flow. Behind the zone through which the thread passes the walls 7 converge to a small slit which is divided into a pair of elongated rectangular outlet slits 20 for the gas, for instance by means of a triangular flow dividing member 8. The direction of the flow of the gases leaving the apparatus is indicated by two arrows. This means provides not only better adherence of the current to the wall but also makes adjustment of over-pressure in the cooling zone for different current rates possible, so that an adjustment of the pressure in the thread take-up chamber can be accomplished to a large extent without control of pressure equalization. By decreasing the equalization current we achieve a quiet thread course. Disturbances are also eliminated from the outside. When profiles are used which have no constant speed in vertical direction, the side walls of the shaft have to be constricted to a smaller slit in the range of lower velocities.

Excess in pressure and thermal updraft make it neces sary to close the cooling zone towards the nozzle at the top and the tubular shaft towards the bottom. In this operation the cooling current is brought in its direction closely to the thread. The connection 9 to the nozzle may be, for instance, a mixing nozzle in order to eliminate turbulence and to obtain well defined flow conditions. The connecting member 10, which leads to the closed shaft taking up the thread, permits to guide the cooling stream in its direction up to the front edge of the lateral walls. The tubular shaft is packed to the shaft opening. When greater blowing velocities are used it is advantaegous to provide a mixing nozzle at this place as well. The upper and lower closures are divided and may be opened and closed with means similar to 8.

The material for making the confining walls, particularly the front of the device, may be polyester reinforced with glass fiber. Observation panels 22 are provided.

At 24, the upper wall and at 26 the lower wall of the apparatus are shown. The spinning nozzle, not forming part of the inventive apparatus, is shown in broken lines at 27. At 28, lateral hinges are shown by means of which the system can be opened for repairs, cleaning and adjustments.

It should be understood that the process according to the invention is in principle useful for spinning inorganic melts as well, although it goes without saying that some adaptations in the apparatus and in the physical parameters will have to be provided.

The spinning device according to the invention has important advantages when compared with known devices, and the quality of the threads is very much improved. The silk which can be spun is practically free of unevenness of the cross-section (titer).

It was for instance, possible to measure unevenness parameters of 0.5 by means of conventional capacitive test devices (of Swiss make, termed Uester tester) whereas known processes yield values of 0.8 to 1. Obviously, the accomplishment is quite remarkable.

What is claimed is:

1. In a process for melt-spinning thread, the steps of directing thread, issuing from a spinning nozzle, longitudinally through an elongated cooling zone of predetermined length and width having in the region of said nozzle an inlet end for receiving thread from the nozzle and distant from the nozzle an outlet end through which the thread leaves the cooling zone, while maintaining the thread in a non-deflected condition as it moves through the cooling zone from the inlet to the outlet end thereof, and simultaneously with the movement of the thread through the cooling zone, directing across the thread from only one side thereof and throughout the entire length and width of the cooling zone a gaseou cooling medium having a non-turbulent, impact-free flow in a direction which at the inlet end of said cooling zone extends perpendicularly across the thread, which at the outlet end of the cooling zone extends across the thread at an angle of -30 displaced from .a line perpendicular to the thread in the direction of thread movement toward the outlet end of the cooling zone, and which between said inlet and outlet ends of said cooling zone gradually changes in inclination from said direction perpendicularly across the thread to the direction of from 10-30 angularly across the thread in the direction of thread movement.

2. In a process as recited in claim 1, introducing the thread into the cooling zone immediately subsequent to issue of the thread from the spinning nozzle.

3. In a process as recited in claim 1, directing the thread from the spinning nozzle in a vertically downward direction through the cooling zone with the latter having its inlet end situated at the top of the cooling zone and its outlet end situated at the bottom of the cooling zone, and with the direction of flow of the gaseous cooling medium being horizontal at the top inlet end of the cooling zone and being inclined downwardly at said angle of 10-30 with respect to the horizontal at said outlet end of said cooling zone, the extent of downward inclination of the direction of flow of the cooling medium gradually increasing from the inlet to the outlet end of the cooling zone.

References Cited by the Examiner ALEXANDER H. BRODMERKEL, Primary Examiner. J. H. WOO, Assistant Examiner, 

1. IN A PROCESS FOR MELT-SPINNING THREAD, THE STEPS OF DIRECTING THREAD, ISSUING FROM A SPINNING NOZZLE, LONGITUDINALLY THROUGH AN ELONGATED COOLING ZONE OF PREDETERMINED LENGTH AND WIDTH HAVING IN THE REGION OF SAID NOZZLE AN INLET END FOR RECEIVING THREAD FROM THE NOZZLE AND DISTANT FROM THE NOZZLE AN OUTLET END THROUGH WHICH THE THREAD LEAVES THE COOLING ZONE, WHILE MAINTAINING THE THREAD IN A NON-DEFLECTED CONDITION AS IT MOVES THROUGH THE COOLING ZONE FROM THE INLET TO THE OUTLET END THEREOF, AND SIMULTANEOUSLY WITH THE MOVEMENT OF THE THREAD THROUGH THE COOLING ZONE, DIRECTING ACROSS THE THREAD FROM ONLY ONE SIDE THEREOF AND THROUGHOUT THE ENTIRE LENGTH AND WIDTH OF THE COOLING ZONE A GASEOUS COOLING MEDIUM HAVING A NON-TURBULENT, IMPACT-FREE FLOW IN A DIRECTION WHICH AT THE INLET END OF SAID COOLING ZONE EXTENDS PERPENDICULARLY ACROSS THE THREAD, WHICH AT THE OUTLET END OF THE COOLING ZONE EXTENDS ACROSS THE THREAD AT AN ANGLE OF 10-30* DISPLACED FROM A LONE PERPENDICULAR TO THE THREAD IN THE DIRECTION OF THREAD MOVEMENT TOWARD THE OUTLET END OF THE CIILING ZONE, AND WHICH BETWEEN SAID INLET AND OUTLET ENDS OF SAID COOLING ZONE GRADUALLY CHANGES IN INCLINATION FROM SAID DIRECTION PERPENDICULARLY ACROSS THE THREAD TO THE DIRECTION OF FROM 10-30* ANGULARLY ACROSS THE THREAD IN THE DIRCTION OF THREAD MOVEMENT. 